Amplification with high efficiency



Aug. 22, 1944.- J. w. M'cRAE 2,356,331

' AMPLIFICATION WITH HIGH EFFICIENCY Filed od. 1o, 1941 NODE SUPPL y PHASE SHIFT ATTO/#MEV atented Aug. 22, i; .-1

AUNITED .STATES PATENT OFFICE-'- I mm1'. oa'rroav million James W. Moline, Neptune, Ng., assigner ggg Telephone La York, N. Y., a corporation of New York application omini 1e, 1941, sum No. 414,439 m omda my 11, 1941 y s claim.'

l The present invention relates to power amplii'ier circuits for radio transmission or similar purposes, with special provision for reducing distortionl and increasing eillciency of operation.

This is a continuation in part of my prior application Serial No. 352,722,1iled August 15, 1940, now Patent No. 2,298,960, October 13, 1942.

A feature of the invention is the use of an electron multiplier type of amplifier as a power amplifier, with circuit provisionsfor reducing distortion and increasing eiilciency.

Electron multipliers, as is known, permit of very large gains and have the'advantage ofnot requiring electrodes of individual stages to be maintained at alternating current potentials. This makes them especially suited to high freq ency amplification. Moreover, one of their characteristics is that the anode potential of the final or output stage has practically no effect on the anode current, at least in the normal operating range. This fact is favorable to the transmission through the multiplier of short pulses of current which retain their form under nearly complete control of the input circuit. The u se of the short pulses permits high emciency to be {abtained in the output stage which couples to the oad. A feature of the invention is the association of two electron multipliersof the power amplifier type in a circuit in a manner-to givehigh efiiciency of signal power amplification.

The invention also lcomprises assfeatures the use of over-allnegative feedback at radio frequency and, therewith or separately, envelop fre'- quency feedback around the initial stage to reduce noise and distortion. 4 l

These and the other features and the various objects of the.' invention will appear more fully from the following detailed description taken in connection with' the accompanying drawing in which the single figure is a schematic circuit diagram of an amplifying system according to the invention.

In the drawing two electron vmultipliers 85 and l0, which may be identical in construction, are associated together to form a Doherty ampliner of the general conguration disclosed in United States Patent 2,210,028, August 6, 1940, but using electron multipliers in place of triodes. y

The electron multiplier tube of itself forms no part oi' the present vinvention but may be of lany suitable construction, the preferred embodiment being in accordance with the disclosure in my copending application Serial No. 371,124, filed December 21, 1940, now Patent 2,279,835, April (ci. lfm-rmV Asource shown in the form of battery I3 applies.

steady positive voltage to the emitters, increasing in valuefrom emitter to. emitter throughout the tube. A voltage divider or potentiometer ,i4 may be used for applying potentials to certain of the electrodes. In the case of the later stages which draw more power from the supply it may be advantageous to ,use sections of the battery as i'known practice. The emitterv plates are bypassed to ground through large condensers I9.

The starter section includes an input circuit comprising the control grid 8, input coupling 69, 1li, bias battery Il and cathode resistor I1 which is shown shunted by capacity I8 (which may be 26 omitted where not necessary) and cathode 1. Thissection includes an output circuit comprising first emitter plate l, portion of resistor I4, cathode network I'I, I8 and cathode 1. The battery f I l applies such arlarge negative potential to the 30 grid that class B or class C operation is secured. That is, transmission through the starter section consists of pulses of half cycle or smallerduration.

In the case of a modulatedhigh frequency input wave, the cathode network I1, I8 is preferably adjusted to vary the control grid bias at the envelope vor signal frequency. Rectification4 in the'plate circuit oi the starter section causes a detected current o f the signal frequency to flow 40 grid bias which permits' .only the positive tips of the high frequency wave to be transmitted. For this use, condenser Il acts as a radio frequency by-pass. At the same time, resistance Il and condenser Ilv provide negative feedback at the signal frequency. This negative'feedback compensates for distortion in the starter section and the varying bias provides the short impulses that are favorable for securing highly efllcient operationv of the output or anode section as will be 5. described later.

Grid I is biased to a positive potential to accelerate electrons toward the emitter 5. Condensers Il, 2i are blocking or by-pass condensers.

r In the output or anode section the nnal emitter iindicated in the diagram. It would be obvious to employ other types of voltage supply in view of v through resistance I1, thus producing a varying i Il is l at direct current ground., Screen II is positive with respect to emitter I0, and anode I2 is maintained at average potential more positive than that of screen I I by anode supply 1,3.

A negative feedback connection is made through lead 5I, stopping condensers 52, and loss network' 53, which may be adjustable, from anode i2 to control grid 8 for producinglarge negative feedback for reducing noise and distortion in the multiplier in accordance with the teachings of Black Patent 2,102,671, December 21, 1937.

The input waves, which may be signal modulated radio frequency waves or other type, are applied across the input coupling resistor il. From this they are applied to the multiplier inputs in parallel, a quarter wave-length line BI being inserted to the input to multiplier 60, in accordance with the Doherty disclosure. The input circuit is coupled in each case through a series capacity 69, the inductance Il being a radio frequency lchoke.

The outputs of the multipliers B5 and It are Iconnected to the output circuit or load 12 which may be a tuned circuit, such as an antenna, or may be of other type. Alternatively this load may be the input of a succeeding amplifier stage and may be untuned. The voltage for thefinal .to said multipliers, lmeans causing one of said anode of each multiplier is obtained from suitable supply 13 such as a rectiiier to lwhich connection is made by way of radio frequency choke 1I. 'I'he quarter wave-length line 'Il 'is inserted between the output of multiplier t5 and the load in accordance with the teachings of the Doherty patent. The feedback connection 6I provides negative feedback around the two multipliers .for increasing the linearity of the circuit.

The electron multipliers are especially suited to use in a Doherty circuit because of their high gain and ability. to operate with short pulse excitation.

The high gain makes possible modulation at low power level and the short 'pulse operation results in high eiliciency. Moreover, as pointed out above, the lack of tuned interstage circuits in the multiplier makes possible large gain with preservation of the wave form of the pulses and the negative feedback also increases the linearity of the ampliner,

What is claimed is:

1. In a high efliciency high gain amplifying system for lamplitude-modulated oscillations, a

first multistageelectron multiplier, a second multistage` electron multiplier, a source of modulated oscillations of varying amplitude, means Acausing each of said multipliers to transmit impulses of and means including a quarter wave-length netv work cooperating with said one multiplier for causing the other of said multipliers to operate, during at least a portion of the modulation cycle, at4 a substantially constant oscillatory output voltage while supplying varying current oscillatory energy to said load.

2. In an amplifying system for high frequency amplitude-modulated waves, a pair of multistage electron multipliers having their inputs coupled to Vsaid source, means to bias their inputs to cause operation of their output stages with current interruption for a major fraction of the high frequency cycle, a load circuit common multipliers to operate with a variable voltage across its output stage and means cooperating with said one multiplier for causing the output stage of-'the other multiplier to operate during at least a portion of the modulation cycle at a substantially constant output voltage while sup- Flying varying current energy to said load.

`3. A system according to claim 2 including an inverse high frequency feedback connection from an output point common to both multipliers, to the input of one of said multipliers.

4. In an amplifying system, a work circuit, a multistage electron multiplier having its output stage coupled to said work circuit and supplying thereto high frequency oscillations of constant amplitude during at least a portion of the cycle of operation, a second and similar electron multiplier having its output stage separately coupled to said work circuit and supplyingthereto high frequency oscillations of signal-dependent amplitude, a quarter wave-length network included in the coupling between the output of one of said multipliers and said work circuit and means controlling the relative phases of the oscillations from said multipliers whereby they combine in phase in said work circuit.

5. In an amplifying system, a source of amplitude-moduiated high frequency waves, a pair of multistage electron multipliers having their input stages coupled to said source., bias means lpreventing current fiow in the input stages of said multipliers except for a fractional part of the positive half of the high frequency cycle, whereby the output stages of said multipliers conduct current only during correspondingA portions of the high frequency cycle, a load circuit, circuits respectively coupling the output circuits of said multipliers to said load circuit, impedance inverttained substantially constant in the presence of currents of varying amplitudes in the outpu stage of the other multiplier,

. JAMES W. MCRAE. 

